1. Field of the Invention:
The present invention relates to a liquid-droplet jetting apparatus, such as an ink-jet printer having a nozzle, which is capable of jetting a liquid droplet, and relates to a liquid-droplet jetting method with respect to such an ink-jet printer for preventing jetting failure due to the drying of the liquid in the vicinity of the opening of the nozzle.
2. Description of the Related Art:
A conventional ink-jet printer is provided with a carriage on which a recording head is mounted. The recording head has a plurality of nozzles for jetting (discharging) ink formed therein, and the ink is filled in pressure chambers communicating with the nozzles, respectively. A drive pulse for jetting the ink is applied to a piezoelectric actuator to deform a deformable portion of the piezoelectric actuator so as to increase and decrease the volume of the pressure chambers, which in turn imparts jetting pressure to the ink in the pressure chambers. This makes the ink to be jetted from the nozzles onto a recording medium while the carriage moves reciprocally.
However, in the recording head, which performs the recording by jetting the ink from the nozzles, there arises a problem such that printing failure is caused by a solvent in the ink (water or the like) which is gradually dried, and thus the ink becomes viscous during a period of time during which no printing is performed and/or in a nozzle through which the ink is jetted less frequently, causing the size of a droplet of the ink (ink droplet) to be smaller than the intended size and/or the ink is jetted less smoothly or less satisfactorily, thereby reducing the printing performance. In such a case, a so-called maintenance operation is performed before performing the printing and/or during the printing operation. The maintenance operation includes, for example, a flushing operation (preliminary jetting) in which the carriage is forcibly or periodically moved to and stand-by at a flushed-ink receiving section located in a non-printing area and then the drive pulse is applied so as to jet the ink forcibly from all the nozzles to perform the flushing; a purge operation in which the carriage is moved to a cap section and then a negative pressure is imparted to the nozzles, thereby forcibly suck and remove air bubbles and/or foreign substance from the nozzles; and the like.
Although the purge operation and flushing operation are effective in removing the foreign substance present or mixed in the ink such as air bubbles, there are problems such that the printing speed is decreased and the ink must be consumed unnecessarily for the non-printing operation because the printing operation must be interrupted to move the carriage to the non-printing area located outside the printing area. In view of these problems, Japanese Patent Application Laid-open No. 2000-85125 and Japanese Patent No. 3613297 (corresponding to U.S. Pat. No. 6,431,674) describe an ink-jet printer in which the ink is prevented from drying and becoming viscous by applying, to the actuator during a period of time in which no ink-jetting is performed, a non-jetting drive pulse which is different from a drive pulse for jetting the ink onto a recording medium and which is a pulse to an extent that no ink is jetted thereby, so as to minutely vibrate a meniscus of the ink (ink meniscus) in the vicinity of the opening of nozzles, thereby preventing the ink from drying and becoming viscous. The term “ink meniscus” means a surface of the ink exposed in the vicinity of the nozzle opening.
In the ink-jet printer described in Japanese Patent Application Laid-open No. 2000-85125, a predetermined electric potential is applied, prior to the ink-jetting, to the actuator (described as “piezoelectric vibration element” in Japanese Patent Application Laid-open No. 2000-85125) such that operations are alternately performed in which the ink meniscus is pulled (drawn) into and pushed back between two positions, namely a reference position and pull-in position, respectively. The reference position is located at a portion further drawn back inside the nozzle opening (position further drawn back on the side of pressure chamber than the nozzle opening surface), and the pull-in positions is located further drawn back inside the nozzle opening with respect to the reference position. By performing such a control, the ink meniscus is minutely vibrated so as to agitate the ink at the nozzle opening, thereby preventing the ink from being dried and becoming viscous.
In the ink-jet printer described in Japanese Patent No. 3613297, the ink meniscus is minutely or slightly vibrated in a minimum cycle in a state that the ink-jet printing apparatus stands still, thereby suppressing the load to the actuator (described as “piezoelectric element” in Japanese Patent No. 3613297) as much as possible while preventing the clogging of the nozzle. Further, the ink is continuously vibrated minutely just before the printing operation is started (resumed), thereby preventing the clogging of the nozzle assuredly.